Electromagnetically actuated brake

ABSTRACT

A brake in which a cam expands brakeshoes into engagement with a rotating brake drum when the cam is turned by a motiontransmitting train connected to an annular electromagnet freely movable on the shaft which carries the drum. The magnet stands still when not energized and is axially attracted toward an armature disc on the shaft and angularly displaced by the rotating disc when energized. Full frictional engagement between the annular pole face of the magnet and the opposite face of the armature disc could block the brake and is prevented by a setscrew on the brake drum which deflects a small abutment portion of the disc axially toward the pole face.

Inventor Ernst Menzi Wldnau, Switzerland Appl. No. 838,525 Filed July 2,i969 Patented Sept. 14, 1971 Assignee Ernst Menzl A.G. Wldnau,Switzerland Priority July 5, 1968 Austria A65 10/68 ELECTROMAGNETICALLYACTUATED BRAKE 6 Claims, 6 Drawing Figs.

Field of Search [56] References Cited UNITED STATES PATENTS 2,068,6541/1937 Cadman 188/164 X 2,290,406 7/1942 Chambers 188/164 2,650,6829/1953 Oetzel 188/164 3,458,022 7/1969 Reiff 188/161 X Primary ExaminerDuane A. Reger Attorney-Kelman and Herman ABSTRACT: A brake in which acam expands brakeshoes into engagement with a rotating brake drum whenthe cam is turned by a motion-transmitting train connected to an annularelectromagnet freely movable on the shaft which carries the drum. Themagnet stands still when not energized and is axially attracted towardan armature disc on the shaft and angularly displaced by the rotatingdisc when energized. Full frictional engagement between the annular poleface of the magnet and the opposite face of the armature disc couldblock the brake and is prevented by a setscrew on the brake drum whichdeflects a small abutment portion of the disc axially toward the poleface.

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INVENTOR Ernsf Menzz BY 'WMI/ Q III/1111111111 IIIIIIIIIIIAITT'ZPATENIEDsEH 4mm 3504541 sum 2 0F 2 INVENTOR. Ernsl" Menu By W M .1ELECTROMAGNETICALLY ACTUATED BRAKE BACKGROUND OF THE INVENTION Thisinvention relates to electromagnetically actuated brakes, and morespecifically to brakes in whichcooperating brake elements on asupporting structure and on a shaft rotatably mounted on the supportingstructure are engaged in response tothe energizing of an electromagnet.

More specifically, this invention is concerned with improvements in abasically known type of brake arrangement in which an electromagnet isnormally stationary on the supporting portion of a machine, but iscoupled to a rotating machine part when energized so that it isangularly displaced relative to the axis of rotation, and amotion-transmitting train engages the braking mechanism in response tothe angular movement of the electromagnet.

Known applications of such brakes include brakes for vehicles and forvarious machines, and the term machine," as used hereinafter, will beunderstood to include vehicles, the supporting structure of the vehiclebeing constituted by the frame and body, and the brake being used forimpeding rotation of a wheel.

The known brakes of the type described have a tendency to engage quitesuddenly. The resulting sudden blocking of a vehicle wheel or othermachine part is usually undesirable, and it has not been possibleheretofore to achieve the reliably smooth application of a graduallyincreasing braking force as is necessary in vehicle brakes, but also inother applications.

A primary object of the invention is an improvement in the basicallyknown electromagnetically actuated brake arrangement described abovewhich reliably provides the desired gradual engagement of the brake whenthe magnet is energized, and avoids sudden blocking of the rotatingmachine part.

SUMMARY OF THE INVENTION With this object and others in view, as willhereinafter become apparent, the invention provides a modification of anarrangement in which a shaft is rotatable on a support about an axis,and an electromagnet is mounted on the support for axial movement andfor angular displacement relative to the axis. An armature member whichhas an engagement face opposite a pole face of the electromagnet ismounted on the shaft for rotation therewith, and respective portions ofthe two faces, circumferentially and radially coextensive, bound anairgap between the armature member and the electromagnet. When theelectromagnet is energized, it is axially attracted by the magneticfield toward the armature member and angularly displaced about the axiswhen the shaft rotates. Cooperating brake elements on the shaft and onthe support are coupled to the electromagnet in such a manner that theyare engaged and thereby impede the rotation of the shaft in response tothe an gular displacement of the electromagnet.

A basic feature of this invention is a protuberance on one of the twoopposite faces, preferably the engagement face of the armature member,which has an axial dimension sufficient to abuttingly engage the otherface, preferably the pole face of the electromagnet, when the latter isattracted toward the armament member and thereby to prevent frictionalengagement of more than a small fraction of the coextensive portions ofthe aforementioned engagement and pole faces. An axially terminalabutment face on the protuberance thus is the only element on thearmature member which can make frictional contact with theelectromagnet, and the area of this abutment face is made very muchsmaller than the area of each of the coextensive face portions.

Other features and many of the attendant advantages of this inventionwill readily become apparent when the same is better understood from thefollowing detailed description of a preferred embodiment when consideredinconnection with the appended drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 shows an armature disc and an annular electromagnet of theapparatus of FIG. 5 in a partly enlarged, axially sectional view;

FIG. 2 shows the device of FIG. 1 in a radial view in a differentcondition;

FIG. 3 shows the disc of FIGS. 1 and 2 in axial end view together withassociated elements;

FIG. 4 shows the device of FIG. 3 in fragmentary axial section on theline IV-IV, and on a larger scale;

FIG. 5 shows a brake arrangement of the invention in axial section; and

FIG. 6 shows a portion of the apparatus of FIG. 5 in axial end view fromthe right.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing indetail, and initially to FIGS. 5 and 6, there is shown as much of thepartly conventional wheel-supporting structure of a truck as is neededfor an understanding of this invention.

A brake drum 13 of conventional shape is fixedly attached to a shaft 6by means of a flange 7. A cam 12 is radially spaced from the shaft axisand rotatable on a sheet metal cover 15 which is an element of thesupport structure of the vehicle, not otherwise shown. Two brake shoes11 are mounted on the cover 15 by means of anchor pins 16 and are biasedaway from the brake drum 13 by a helical tension spring 17 whichconnects the ends of the shoes 11 adjacent the cam 12 and remote fromthe pins 16.

A gear segment 10 is fixedly fastened to the cam 12 and meshes with anannular gear rim 9 on a spider 8 which is freely movable on the shaft 6.The gear teeth of the rim 9 are axially longer than the teeth of thegear segment 10 to permit limited axial movement of the spider 8 on theshaft 6. The spider 8 carries an annular electromagnet 2 which has aflat annular pole face perpendicular to the axis of rotation of theshaft 6 and centered in the axis. An annular armature disc 1 ofmoderately resilient and flexible mild steel is attached to the flange 7by four screws 5 spaced about 72 apart on a common circle about theshaft axis, as is best seen in FIG. 3. Some dimensions have beendistorted in FIGS. 1 to 4 for a clearer representation of certainfeatures of the invention.

The disc 1 is flat in the relaxed condition illustrated in FIGS. 1 and5, and its engagement face opposite the radially and circumferentiallypartly coextensive pole face of the electromagnet 2 extends in a radialplane relative to the axis of the shaft 6. The head of a setscrew 4 isaccessible through the bottom wall of the brake drum 13 which providesan enveloping casing for the disc 1, the electromagnet 2, and theillustrated end portion of the shaft 6. The shank of the screw 4 isthreadedly received in an axial bore of the flange 7, and the free endof the screw may abuttingly engage the normally radial face of the ring1 directed axially away from the electromagnet 2 in the corner of theregular pentagon otherwise defined by the screws 5, as is shown in FIGS.3 and 4.

When the head of the screw 4 is turned by means of a tool insertedthrough the opening in the brake drum 13, a portion 3 of the disc I isdeflected by the motion-transmitting free shank end from the radialplane in which the remainder of the disc is held by the screws 5, as isshown in FIG. 2 with substantial dimensional exaggeration for the sakeof clarity.

A weak return spring, not shown, normally holds the electromagnet 2 inthe illustrated position in which a uniform airgap 5 separates theopposite faces of the disc 1 and of the electromagnet 2 when the disc isin the relaxed condition of FIG. 1. When the disc is partly deflected bythe screw 4 so that a part of its engagement face is obliquely inclinedrelative to the shaft axis, the distance 6, between most of theengagement face and the pole face of the electromagnet 2 is stilluniform, but the airgap between the deflected disc portion and themagnet is reduced to a smaller axial width 8 (FIG. 2).

Although the actual difference between 8, and 8 is much smaller thanwould be apparent from FIG. 2, and is normally only a small fraction .of6,, the protuberance formed by the deflected disc portion is ofsufficient axial height to prevent frictional engagement of more than avery small fraction of the radially and circumferentially coextensiveportions of the annular, opposite faces when the magnet is energized.The torque transmitted from the armature disc 1 to the energizedelectromagnet 2 is thus predominantly a function of the readilycontrolled current in the winding of the electromagnet, and only to asmall extent a function of the frictional forces transmitted between theopposite faces of the armature disc and of the electromagnet and notamenable to control in a convenient manner.

The brake arrangements of the invention can therefore be engagedsmoothly and are free from the blocking tendency characteristic ofsimilar known devices in which broad faces of a magnet and of anarmature engage each other when the magnet is energized.

The effective axial length of the protuberance provided by the discportion 3 can be controlled simply and very precisely by means of thesetscrew 4 to determine the width of the residual gap remaining betweenthe pole face of the magnet and most of the opposite radial face of thedisc 1 when the protuberance abuts against the pole face and makescontact with the pole face over an abutment area which is only a verysmall fraction of the disc face.

While the invention has been described with reference to an expandingbrake, more specifically a drum brake, those skilled in the art willmodify it for adaptation to contracting brakes, such as band brakes, andto disc brakes, to mention only brakes now in common use on automotivevehicles. Applications to other machines and variations in theillustrated device will readily suggest themselves on the basis of theabove teachings.

A protuberance may thus be provided on the pole face of the magnet 2,opposite a flat face of the disc 1. More than one setscrew 4 may beprovided if so desired although a single protuberance, as illustrated,has been found quite adequate. A sufficient number of screws 4 may givethe disc 1 an undulating shape in which axial stresses are moreuniformly distributed about the circumference than in the illustrated embodiment.

The advantages of the invention are equally available in arrangements inwhich the magnet, the armature member or both are not annular, or wherean annular pole piece is backed by a magnet ofa shape very differentfrom that illustrated.

What is claimed is:

1. in a machine including a support; a shaft rotatable on said supportabout an axis; an electromagnet mounted on said support for axialmovement and for angular displacement relative to said axis, said magnethaving a pole face; and armature member having an engagement faceopposite said pole face, said armature member being mounted on saidshaft for rotation therewith, respective portions of said faces beingcircumferentially and radially coextensive and axially bounding anairgap between said armature member and said electromagnet, saidelectromagnet when energized being axially attracted toward saidarmature member and angularly displaced about said axis when said shaftrotates, and cooperating engageable brake means on said shaft and onsaid support responsive to said angular displacement of saidelectromagnet for engaging said brake means and for thereby impeding therotation of said shaft, the improvement which comprises:

a. a protuberance on said engagement face of an axial dimensionsufficient to abuttingly engage said pole face when said electromagnetis attracted toward the armature member and to prevent frictionalengagement of more than a small fraction ofsaid coextensive portions,

b. said protuberance having an axially terminal abutment face positionedfor frictional engagement with said pole face, the area of said abutmentface being very much smaller than the area of said coextensive portions,

c. said coextensive portion of said engagement face being annular aboutsaid axis and in part obliquely inclined relative to said axis, wherebya part of said portion of the engagement face is nearer said pole facethan the remainder of said engagement face, said part constituting saidabutment face.

2. In a machine including a support; a shaft rotatable on said supportabout an axis; an electromagnet mounted on said support for axialmovement and for angular displacement relative to said axis, said magnethaving a pole face; an armature member having an engagement faceopposite said pole face, said armature member being mounted on saidshaft for rotation therewith, respective portions of said faces beingcircumferentially and radially coextensive and axially bounding anairgap between said armature member and said electromagnet, saidelectromagnet when energized being axially attracted toward saidarmature member and angularly displaced about said axis when said shaftrotates, and cooperating engageable brake means on said shaft and onsaid support responsive to said angular displacement of saidelectromagnet for engaging said brake means and for thereby impeding therotation of said shaft, the improvement which comprises:

a. a protuberance on one of said faces of an axial dimension sufficientto abuttingly engage the other face when said electromagnet is attractedtoward the armature member and to prevent frictional engagement of morethan a small fraction of said coextensive portions,

b. said protuberance having an axially terminal abutment face positionedfor frictional engagement with said other face, the area of saidabutment face being very much smaller than the area of said coextensiveportions,

0. the coextensive portion of said one face being annular about saidaxis and substantially extending in a plane radial relative to saidaxis, said protuberance projecting from said radial plane toward saidother face.

3. In a machine including a support; a shaft rotatable on said supportabout an axis; an electromagnet mounted on said support for axialmovement and for angular displacement relative to said axis, said magnethaving a pole face; an armature member having an engagement faceopposite said pole face, said armature member being mounted on saidshaft for rotation therewith, respective portions of said faces beingcircumferentially and radially coextensive and axially bounding anairgap between said armature member and said electromagnet, saidelectromagnet when energized being axially attracted toward saidarmature member and angularly displaced about said axis when said shaftrotates, and cooperating engageable brake means on said shaft and onsaid support responsive to said angular displacement of saidelectromagnet for engaging said brake means and for thereby impeding therotation of said shaft, the improvement which comprises:

a. a protuberance on said engagement face of an axial dimensionsufficient to abuttingly engage said pole face when said electromagnetis attracted toward the armature member and to prevent frictionalengagement of more than a small fraction of said coextensive portions,

b. said protuberance having an axially terminal abutment face positionedfor frictional engagement with said pole face, the area of said abutmentface being very much smaller than the area of said coextensive portions,

c. said armature member being a disc of flexible material,

and g d. control means for flexing a portion of said disc axially towardsaid pole face, the flexed portion constituting said protuberance.

4. in a machine as set forth in claim 2, said one face being saidengagement face.

5. In a machine as set forth in claim 2, controlling means for varyingsaid axial dimension.

6. ln a machine as set forth in claim 3, a casing enveloping said disc,said electromagnet and a portion of said shaft, said casing beingmounted on said shaft for rotation therewith, and said control meansincluding a control member movably mounted in said casing and accessiblefrom outside said casing for causing the movement of the same, andmotion-transmitting means connecting said control member to said discfor flexing the same in response to said movement of the control member.

1. In a machine including a support; a shaft rotatable on said supportabout an axis; an electromagnet mounted on said support for axialmovement and for angular displacement relative to said axis, said magnethaving a pole face; and armature member having an engagement faceopposite said pole face, said armature member being mounted on saIdshaft for rotation therewith, respective portions of said faces beingcircumferentially and radially coextensive and axially bounding anairgap between said armature member and said electromagnet, saidelectromagnet when energized being axially attracted toward saidarmature member and angularly displaced about said axis when said shaftrotates, and cooperating engageable brake means on said shaft and onsaid support responsive to said angular displacement of saidelectromagnet for engaging said brake means and for thereby impeding therotation of said shaft, the improvement which comprises: a. aprotuberance on said engagement face of an axial dimension sufficient toabuttingly engage said pole face when said electromagnet is attractedtoward the armature member and to prevent frictional engagement of morethan a small fraction of said coextensive portions, b. said protuberancehaving an axially terminal abutment face positioned for frictionalengagement with said pole face, the area of said abutment face beingvery much smaller than the area of said coextensive portions, c. saidcoextensive portion of said engagement face being annular about saidaxis and in part obliquely inclined relative to said axis, whereby apart of said portion of the engagement face is nearer said pole facethan the remainder of said engagement face, said part constituting saidabutment face.
 2. In a machine including a support; a shaft rotatable onsaid support about an axis; an electromagnet mounted on said support foraxial movement and for angular displacement relative to said axis, saidmagnet having a pole face; an armature member having an engagement faceopposite said pole face, said armature member being mounted on saidshaft for rotation therewith, respective portions of said faces beingcircumferentially and radially coextensive and axially bounding anairgap between said armature member and said electromagnet, saidelectromagnet when energized being axially attracted toward saidarmature member and angularly displaced about said axis when said shaftrotates, and cooperating engageable brake means on said shaft and onsaid support responsive to said angular displacement of saidelectromagnet for engaging said brake means and for thereby impeding therotation of said shaft, the improvement which comprises: a. aprotuberance on one of said faces of an axial dimension sufficient toabuttingly engage the other face when said electromagnet is attractedtoward the armature member and to prevent frictional engagement of morethan a small fraction of said coextensive portions, b. said protuberancehaving an axially terminal abutment face positioned for frictionalengagement with said other face, the area of said abutment face beingvery much smaller than the area of said coextensive portions, c. thecoextensive portion of said one face being annular about said axis andsubstantially extending in a plane radial relative to said axis, saidprotuberance projecting from said radial plane toward said other face.3. In a machine including a support; a shaft rotatable on said supportabout an axis; an electromagnet mounted on said support for axialmovement and for angular displacement relative to said axis, said magnethaving a pole face; an armature member having an engagement faceopposite said pole face, said armature member being mounted on saidshaft for rotation therewith, respective portions of said faces beingcircumferentially and radially coextensive and axially bounding anairgap between said armature member and said electromagnet, saidelectromagnet when energized being axially attracted toward saidarmature member and angularly displaced about said axis when said shaftrotates, and cooperating engageable brake means on said shaft and onsaid support responsive to said angular displacement of saidelectromagnet for engaging said brake means and for thereby impeding therotation of said shaft, the improvement which comprises: a. aprotuberance on Said engagement face of an axial dimension sufficient toabuttingly engage said pole face when said electromagnet is attractedtoward the armature member and to prevent frictional engagement of morethan a small fraction of said coextensive portions, b. said protuberancehaving an axially terminal abutment face positioned for frictionalengagement with said pole face, the area of said abutment face beingvery much smaller than the area of said coextensive portions, c. saidarmature member being a disc of flexible material, and d. control meansfor flexing a portion of said disc axially toward said pole face, theflexed portion constituting said protuberance.
 4. In a machine as setforth in claim 2, said one face being said engagement face.
 5. In amachine as set forth in claim 2, controlling means for varying saidaxial dimension.
 6. In a machine as set forth in claim 3, a casingenveloping said disc, said electromagnet and a portion of said shaft,said casing being mounted on said shaft for rotation therewith, and saidcontrol means including a control member movably mounted in said casingand accessible from outside said casing for causing the movement of thesame, and motion-transmitting means connecting said control member tosaid disc for flexing the same in response to said movement of thecontrol member.